Sankin-koutai (参勤交代) was a policy by the Shogunate for most of the Edo period where various Daimyo had to move periodically between Edo and his territory, typically spending alternate years in each place. His wife and heir were required to remain in Edo as hostages.

This phrase is probably a reference from a story of the Matsudaira Clan (松平氏). Otegine was highly treasured by the Matsudaira Clan, so if there's even a speck of rust on the spear a maintenance would be immediately carried out. At that time, if the sword maintainer found and repaired the rust, the Matsudaira Clan would give them a raise in salary as an incentive. However, since the appearance of rust meant the maintainer was negligent in the upkeep, admitting it was equal to shaming themselves. Thus, if there was slight rust on the spear during inspection, the maintainer would say that it was not rust and repair it in secret while refusing any pay raise from the clan.